GRP and steel: Comparison of two materials

What are the properties of steel and glass fibre- reinforced plastic? We have carefully examined the two materials for you.

Reading time: 4:00 min.

GRP or steel - Which material is the all-rounder?

Whether kitchen utensils such as cutlery and pots, the barbecue in the garden or tools of all kinds: Steel is everywhere. Even on our way to work, because our cars are also made largely of steel. But it is not only in everyday life that we see steel. In the working world, steel is a multi-talent. The material is used in construction, mechanical and plant engineering and energy technology in particular. It provides excellent performance, is easy to shape, universally applicable and extremely long-lasting. So it's no wonder that architects, designers and engineers like to use steel as a material. 

Glass fibre-reinforced plastic is also very popular as a material and its application options are almost unlimited. Whether in the construction, caravan, bus and commercial vehicle industries, GRP is impressive thanks to its light weight, high strength and resistance to weathering. The answer to the question "GRP or steel - which material is the all-rounder?" depends on the application where the material is used, because the required properties also depend on it. 

What exactly is steel?

Steel is largely made of iron. Iron is naturally very susceptible to rust. Rust is caused by iron reacting by oxidation with oxygen in the presence of water to form iron oxide. In general, steel is an iron-carbon alloy containing less than 2.06% carbon. Steel is hard, elastic and impact resistant. Steel can be cast, forged, pressed and rolled. There are also thousands of different alloys. In metallurgy, an alloy is a metallic mixture of two or more chemical elements, at least one of which is a metal. Each alloy has its own special properties so that the steel can be individually adapted to the application. All materials referred to as steels are a structure consisting of the elements iron, other metals, carbon and other non-metals. Different types of steel are generally distinguished. 

Types of steel:

  • General structural steel
  • Machining steel
  • Reinforcing steel
  • Case-hardening steel
  • Spring steel
  • Stainless steel
  • Nitriding steel
  • Acid-resistant steel
  • Tensioning steel
  • Tool steel
  • Knife steel

What's behind glass fibre-reinforced plastic?

Properties of GRP and steel: Comparison of two materials

The biggest problem with the steel is its weight. Even though much has been tried and tested to reduce the weight, no solution is yet in sight. For example, steel sheets in car construction have been produced ever thinner to save weight. But at some point a limit has been reached here, as otherwise the stability is compromised. Glas fibre-reinforced plastic, on the other hand, is very light and at the same time extremely strong and dimensionally stable. However, this depends on the thickness and properties of the resin matrix. The overall structure also plays a role, i.e. whether it is a moulded part, a single sheet or a sandwich with different foams, for example. 
Steel scores highly in its temperature resistance. Whether it's hot temperatures in summer or ice and frost in winter: A bridge construction must withstand all temperatures. As a machine or plant material, steel is exposed to even hotter temperatures. But this is not a problem either: Steel can withstand temperatures of up to 700  °C and even up to 1,100 °C with special alloys. GRP, on the other hand, can withstand temperatures of up to 130 °C, which does appear to be very low compared to steel, but is more than sufficient for the application areas of GRP. 
Steel is therefore optimally protected against heat, but water can become a problem. In the salt spray test, which tests the corrosion resistance of materials, steel forms rust and blisters after just a few hours. Unlike glass fibre-reinforced plastic: Water poses no problems here. GRP shows no damage even after 20 days of testing. 
Similarly, with regard to the cleanability of the materials, in comparison to steel, GRP is very easy to clean as a surface and resistant to cleaning agents. 

Steel - a recyclable but finite raw material

Steel is very durable and even if a steel product has become obsolete, it can easily be recycled and reprocessed without any loss of quality. No material is recycled more often than steel. German steel producers recycle around 20 million tonnes of old steel every year. That is enough steel to build eight new Eifel towers every day.
Nevertheless, the raw material situation does not look good: Although the earth's crust consists of 5% iron, the industry's raw material requirements cannot be met. One reason for this is the increasing steel requirements of the Chinese, Indian and Brazilian economies. Steel production in China alone is growing annually by more than the current total production in Germany. The dramatically changed raw material situation means that prices for steel products continue to rise and steel is in very short supply and expensive compared to other materials. The following therefore applies: Even though steel is an indispensable material in many different industries, we still have to look for a replacement material due to the finite nature of the resource.

Mining of iron | insights by LAMILUX